1. Field of the Invention
The present invention relates to a machine tool of the type wherein a spindle head is adapted to detachably mount thereon a spindle attachment having a tool spindle which is horizontal or inclined relative to a spindle rotatably carried by the spindle head.
2. Discussion of the Prior Art
In a horizontal spindle attachment as used in vertical machine tools of the aforementioned type, an attachment spindle for receiving a cutting tool holder extends perpendicularly to the axis of a tool spindle supported by a spindle head of the machine tool. In order to unclamp the tool holder from the attachment spindle for a tool change operation, the spindle head is moved to engage the rear end of the attachment spindle with an unclamping device and to make the attachment spindle aligned with an actuation rod of the unclamping device, as disclosed in Japanese unexamined, published patent application No. 57-178631.
In the prior art machine tool, when machining is to be performed with the axis of a cutting tool being inclined at 45 degrees, for example, relative to the tool spindle, there is used an angle spindle attachment whose spindle is so inclined. In this case, if an attempt is made to automatically change a tool holder having been held by each angle spindle attachment, the machine tool may have to be provided with one or more unclamping devices which respectively meet the inclination angles of attachment spindles of angle spindle attachments selectively used therein, in addition to that dedicated to a horizontal spindle attachment, or the unclamping device for the horizontal spindle attachment may have to be modified so that an unclamping actuation rod is tiltable. This may disadvantageously result in an increased manufacturing cost of the machine tool as well as in a complicated control.